Cisco Interface Counters and Errors

Use interface counters when links are slow, dropping traffic, flapping, or reporting CRC/input errors.

Quick checks

show ip interface brief
show interfaces status
show interfaces counters errors
show interfaces ethernet0/1

Clear counters for a fresh test

clear counters ethernet0/1

Run this only when you are ready to lose historical counters for that interface.

What to look for

• CRC/input errors: cabling, optic, speed/duplex, or physical-layer issue.
• Output drops: congestion or QoS shaping/policing.
• Interface resets or carrier transitions: link flapping.
• Duplex mismatch on older copper links.

Related

• Cisco Fiber Transceiver Checks
• Cisco Port-Channel